We investigate the genetic causes of two of the major psychiatric disorders: Schizophrenia and Obsessive-Compulsive Disorder (OCD). Schizophrenia has been called "arguably the worst disease affecting mankind, even AIDS not excepted". The worldwide lifetime prevalence of the disorder is about 1% across diverse geographic, cultural, and socioeconomic categories. Obsessive-Compulsive Disorder is a neurobiological disorder which affects 2-3% of the population. Family, twin and adoption studies provide overwhelming but indirect evidence for a significant genetic contribution to the etiology of both disorders. Inheritance is not simple however and most likely involves a number of susceptibility genes and environmental influences. Our goals are: 1)to identify genes for both disorders; 2)to specify the function, and mode of dysfunction, of the involved genes; 3)to define the genotypic and phenotypic heterogeneity of these disorders; and 4)to propose improved treatments for these disorders, based on our genetic findings.